Colorectal carcinoma is the second most frequent cause of cancer mortality in men and women, causing nearly one third of all malignancy-related deaths in North America. It has been estimated that ultimately as many as 6% of Canadians and Americans will develop malignancy in the lower bowel, and over 50% of them will die within 5 years of diagnosis. Many authorities believe that colorectal cancer can be controlled only by preventive measures (1) because there are no realistic prospects of significantly improving the cure rate once the cancer has spread beyond the bowel wall.
Primary prevention, i.e. averting the development of the tumour by altering biological risk factors, is not yet feasible since so little is understood of the etiology of the disease. Alternatively, secondary preventive measures, i.e. detection at an asymptomatic, treatable state, would be possible should an effective screening test be available. Indeed, neoplasms of the lower bowel have the characteristics that make them suitable candidates for the development of a screening test. This is because (i) they are a common cause of cancer-related deaths, and (ii) whereas once the stage of true cancer is reached, and showing symptoms, the mortality rate is over 50%. Removal of bowel neoplasms at their earliest, asymptomatic stage can be done by non-surgical endoscopic polypectomy, without any significant risk. Moreover, it requires at least four to six years before an adenomatous polyp reaches the cancer stage, so there is ample opportunity to detect these neoplasms at their treatable stage. Recent clinical studies document a decrease in mortality in consequence of colorectal cancer screening, as predicted by these theoretical considerations. The problem to-date has been that polyps can be reliably detected only by endoscopy.
Thus, colorectal cancer satisfies each of the following three criteria of a disease considered suitable for a screening program. First, it is a relatively common condition with serious consequences. Second, curative treatment is available when detected at an early stage, i.e. snare polypectomiy through a colonoscope or surgical segmental bowel resection. Third, the prevalence is sufficiently high to justify the expense of a screening program (2).